A concept propagated by hippies and other counter-culture rebels during the tumult of the 60s and 70s. The idea is that people should be free to love each other with no commitment besides what they feel is right.
This was tied in with such cultural landmarks as communes and Woodstock, and lead to quite a few confused young people having as much sex as possible, due to an urge to break old boundaries and rules and explore their newfound "free" sexuality.